I have dropped Mathematica in favor of MaximaMaxima some time ago in order to escape from obscure bugs remaining unfixed and licensing troubles, and have not regretted it since. Now I just came across Qinf, which is a free (as in GPLv2) quantum information suite for Maxima. While the package is still under development it already contains quite a lot useful functions like partial traces, entropy calculation, operator expansion. So if you use Qinf instead of another package relying on a proprietary CAS, you can prevent your code from being trapped.
Copyright 2006--2011 Hendrik Weimer. This document is available under the terms of the GNU Free Documentation License. See the licensing terms for further details.